Evidence for nonlinear resonant mode coupling in the Cephei star HD 180642 (V1449 Aquilae) from CoRoT photometry ^*,**,***

¹ Instituut voor Sterrenkunde, K.U. Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium e-mail: pieter.degroote@ster.kuleuven.be
² LESIA, CNRS, Université Pierre et Marie Curie, Université Denis Diderot, Observatoire de Paris, 92195 Meudon Cedex, France
³ INAF – Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate, Italy
⁴ Laboratoire AIM, CEA/DSM-CNRS-Université Paris Diderot; CEA, IRFU, SAp, Centre de Saclay, 91191 Gif-sur-Yvette, France
⁵ Belgisch Instituut voor Ruimte Aeronomie (BIRA), Ringlaan 3, 1180 Brussels, Belgium
⁶ Institut d'Astrophysique et de Géophysique, Université de Liège, Allée du 6 Août 17, 4000 Liège, Belgium
⁷ Department of Astrophysics, IMAPP, University of Nijmegen, PO Box 9010, 6500 GL Nijmegen, The Netherlands

Received: 3 February 2009
Accepted: 27 May 2009

Abstract

Context. We present the CoRoT light curve of the Cep star HD 180642, assembled during the first long run of the space mission, as well as archival single-band photometry.

Aims. Our goal is to analyse the detailed behaviour present in the light curve and interpret it in terms of excited-mode frequencies.

Methods. After describing the noise properties in detail, we use various time series analyses and fitting techniques to model the CoRoT light curve, for various physical assumptions. We apply statistical goodness-of-fit criteria that allow us to select the most appropriate physical model fit to the data.

Results. We conclude that the light-curve model based on nonlinear resonant frequency and phase locking provides the best representation of the data. Interpretation of the residuals is dependent on the chosen physical model used to prewhiten the data.

Conclusions. Our observational results constitute a fruitful starting point for detailed seismic stellar modelling of this large-amplitude and evolved Cep star.